The present invention relates to microlenses, and more particularly to liquid microlenses.
Most tunable microlenses are either gradient index (GRIN) lenses with the refractive index controlled electrostatically or flexible polymeric lenses with the shape controlled mechanically. Both technologies have inherent limitations that impose severe restrictions on the performance of these existing tunable microlenses.
Tunable gradient index lenses have inherent limitations associated with the relatively small electro-optic coefficients found in the majority of electro-optic materials. This results in a small optical path modulation and, therefore, requires thick lenses or very high voltages to be employed. In addition, many electro-optic materials show a strong birefringence that causes polarization dependence of the microlens properties.
Mechanically adjustable flexible lenses typically have a substantially wider range of tunability than the gradient index lenses. However, they require external actuation devices, such as micropumps, to operate. Microintegration of such devices involves substantial problems, especially severe in the case where a two-dimensional array of tunable microlenses is required.
Attempts have also been made to use other technologies to produce tunable microlenses, such as liquid microlenses controlled through self assembled monolayers (SAMs). Some of these attempts are described in U.S. Pat. No. 6,014,259 to Wohlstadter, issued Jan. 11, 2000, the entirety of which is hereby incorporated by reference herein. Microlenses utilizing self assembled monolayers, however, also suffer from several problems, including severe limitations on material selection and strong hysteresis leading to the failure of the microlens to return to an original shape after a tuning voltage is disconnected. Additionally, none of the above-described microlenses allow for both lens position adjustment and focal length tuning.
A tunable liquid microlens is proposed in the Applicants"" copending U.S. patent application Ser. No. 09/884,605 to Timofei N. Kroupenkine and Shu Yang, filed Jun. 19, 2001, entitled xe2x80x9cTunable Liquid Microlens.xe2x80x9d The tunable liquid microlens of the ""605 application allows for both lens position adjustment and focal length tuning. In one embodiment of an exemplary tunable liquid microlens described in the ""605 application, a droplet of a transparent conducting liquid is disposed on a supporting substrate including a fluorinated polymer, such as a highly fluorinated hydrocarbon. This configuration provides a liquid microlens that is highly tunable and which does not suffer from the well known hysteresis and stick-slip effects, which can occur during electrowetting.
While the ""605 application provides for an exemplary tunable liquid microlens, there remains a need for a tunable liquid microlens that provides for even greater freedom in material selection and excellent tunability while reducing or eliminating contact angle hysteresis and stick-slip effects. This is achieved by an improved tunable liquid microlens that includes an insulating layer, a droplet of a transparent conducting liquid, and, in accordance with the principles of the invention, a lubricating layer disposed on a first surface of the insulating layer and between the droplet and the insulating layer. The microlens also includes a plurality of electrodes insulated from the droplet by the insulating layer and the lubricating layer, the plurality of electrodes being disposed such that they may be selectively biased to create a respective voltage potential between the droplet and each of the plurality of electrodes, whereby an angle between the droplet and a plane parallel to the first surface of the insulating layer may be varied and the droplet may be repositioned relative to the insulating layer.
The tunable liquid microlens with lubrication assisted electrowetting allows for both lens position adjustment and focal length tuning. In addition, the tunable liquid microlens provides for even greater freedom in material selection with no contact angle hysteresis or stick-slip effect while providing excellent tuning control.